I like this idea a lot!
I thought about proposing an additional check in this Jenkins hook to also check the codereview status of the revisions. So that it would update the wikis to the "latest reviewed revision that passes the unit tests". However after the Git migration, mediawiki-core/master wiill only contain reviewed commits anyway, so such check is no longer necessary. Nice :)
Lab's "beta" project (renamed from "deployment-prep") was originally meant to show the next release, not alpha or trunk ("master" or "svn trunk").
I don't think that "beta" should be running on trunk. However it should be relatively easy to set up another labs' project just like "beta" (e.g. named "mw-alpha") which would indeed run on trunk.
Both "mw-alpha" and "mw-beta" would be automatically updated by this Jenkins hook.
Which reminds me, right now we don't have a project for REL1_19 in Jenkins (we should!), previously when we still used phpUnderControl we did monitor the release branches.